FYI, I found that perhaps THE most important thing to be aware of in Reaper if you have multiple tempos and/or time signatures within the same song is to first select Project Settings (Alt + Enter on PC) and then under "Timebase for items/envelopes/markers:" change the default "Beats: position/length/rate" to "Time," (See screenshot)

***Note: this should be done before you import any audio or MIDI into your project!

Once you do this, the tempo of your imported items will not be affected by the projects overall tempo.

Also, when you want to import new items or record and speed up slow down or what have you without affecting pitch, make sure to insert split points at the beginning and end of each section that has/will have a given tempo. This will effectively convert each of the sections into items which you can edit, time stretch, change tempo at will w/o affecting the rest of the track.

Attached Files (Click to download or enlarge) (Only available when you are logged in)
Reaper Timebase.PNG (36.32 KB, 114 downloads)
Last edited by DeaconBlues09; 01/09/18 09:17 PM. Reason: Adding attachment.
Band-in-a-Box 2024. Custom Build Desktop PC W/ Windows 10 Home 64-bit. CPU: Intel Core i5-9600k @ 3.7GHz (6 core x 6 threads) RAM: 16GB DDR4. Storage 238GB SSD + 2.7 TB HDD. GPU: ZOTAC NVIDIA GeForce GTX 1050 Ti 4GB